Blender2Xplane texturing?
I'm Ted. I'm the developer of XPlane2Blender. The best place for this type of question is GitHub's issues page.

XPlane2Blender used to have a feature where it would use a material's texture slots to automatically fill in the TEXTURE path. Blender 2.80 removed Texture Slots so now while a similar feature is being implemented, we're just having people put in the relative file path by hand. Remember not to use spaces. You'll find that in the OBJ settings.



In this image, some Empty or Mesh or other Blender Object has been marked as exportable (or "Root Object" in old 2.79 UI). The name is my_example_object, and its TEXTURE is my_texture.png

XPlane2Blender doesn't check that this file exists so that is up to you.

Read the release notes pages for recent releases of XPlane2Blender as it is currently the best source of documentation on new features.